Method of and apparatus for electromechanicaly producing printing forms from line-originals



March 31, 1959 ELL 2,880,270

R. H METHOD OF AND PARATUS FOR ELECTRO HANICALLY CIN ING FORMS FROMLINE- IGINALS 2 Sheets-Sheet l PRODU G PR N Filed July 10, 1953 5 16 I]f I 21 J/Liifl 9 i 2 /%/A 1 7 INVENTOR. 1 240 05 We ZZ I BY March 1959R. HEL L 2,880,270

A METHOD OF AND APPARATUS FOR ELECTROMECHANICALLY I PRODUCING PRINTINGFORMS FROM LINE-ORIGINALS Filed July 10, 1953 2 SheetsSheet 2 1 45 kAMPLIFIER D CONTROL DEVICE 4 9 AMPLIFIER D ain- DEVICE GRA V/NG TOOL f47 J2 V MOTOR DRUM CA RRY/NG DRUM CARR Y/NG BLANK ORIGINAL 7 TO BEENGRAVED 30 INVENTOR.

United States Patent METHOD OF AND APPARATUS FOR ELECTRO- MECHANICALYPRODUCING PRINTING FORMS FROM LIN E-ORIGINALS Rudolf Hell,Kiel-Dietrichsdorf, Germany, assignor t0 Dr.-Ing. Rudolf HellKommanditgesellschaft, Kiel- Dietrlchsdorf, Germany, a German companyApplication July 10, 1953, Serial No. 367,299

Claims priority, application Germany July 15, 1952 8 Claims. (Cl.1786.6)

This invention is concerned with apparatus for electromechanicallyproducing printing forms from line originals.

In known apparatus employing the principles of picture telegraphy forthe electromechanical production of printing forms, a line-bearingoriginal, for example, a drawing, written matter or a map, whichconsists only of a light and a dark color-generally black andwhite-without any half-tones, is photoelcctrically scanned line forline. To this end, a small area element of the original is isolated andits brightness is measured by a photoelectric cell. When the scanningspot scans a dark area element of the original, the photoelectriccurrent actuates a graving tool which produces a correspondingdepression in the material of the printing form. If, however, a light(white) portion is scanned, the graving tool does not operate. Portionsof the original extending at an angle to the direction of scanningreceive in this manner a stepped contour, but due to the smallness ofthe scanned area elements the steps are not apparent to the unaided eye.

These known methods have the disadvantage that large continuousdepressions in the printing form, representing large white areas of theoriginal and not intended for printing, are nevertheless inked by theresilient inking roller and apply ink to the slightly sagging paper.Consequently, white portions of the original appear partly black in theprint. Moreover, the elastically deformed portions of the inking rollerapply ink to the lateral end faces of the printing portions of the form,and this ink is likewise transferred to the paper and has the effect ofwidening the contours in the print. The latter, then, no longercorresponds exactly to the original.

In chemigraphic methods of making line etchings, in which the sameproblem also arises, the non-printing areas are generally re-cut byhand, or deep-milled in a graving machine. These subsequent treatmentsrequire considerable experience and are time-wasting since it isnecessary in addition to round off, by a subsequent etching step, anyridges left over after the cutting operation. Other known methods employa succession of etching steps to deepen the large non-printing areas ofthe printing form. These repeated etching steps render this methodcumbersome and time-wasting. If these methods were to be applied to theelectromechanical graving of printing forms, it would entail foregoingthe main advantage of this process, which resides in the rapid andautomatic production of the printing form.

According to the present invention, the large continuous non-printingareas of the printing form are deepened during the graving operation, tosuch an extent as to reliably prevent any contact of the inking rolleror of the paper with the bottom of the depressions during printing. Thisis done by increasing the stroke of the graving tool at these points, sothat the tool penetrates more deeply into the material being treatedthan was the case in conventional graving methods. The extra steps2,880,270 Patented Mar. 31, 19 59 ice of subsequently deepening thedepressions by milling or cutting operations are thus eliminated.

The type of graving tool employed is immaterial to the presentinvention; cutting, drilling, milling or heated tools may be employed;alternatively, electrodes graving by means of an electric arc may beused, which burn off or chemically decompose the material to be removed.Therefore, the term graving is intended hereinafter to comprise any kindof treatment of the printing form with any desired tool. It is alsoimmaterial whether the line original and the form are mounted on a flatcarriage or on a drum, and whether the original is scanned across itsthickness or on its surface, that is, whether it is transparent orreflective,

The deepening of a large non-printing area-hereinafter termeddeep-gravingraises a special problem. As is known, the graving toolperforms two movements at right angles to each other: first, a relativedisplacement in the direction of scanning, which may consist of movementof a tool-supporting carriage, or alternatively of a displacement of theform, with the tool remaining stationary; and secondly, a strokeperpendicular to the surface of the printing form. When the scanning ofa black portion of the original terminates, the printing area remainingin the material of the form should likewise be terminated by penetrationof the tool into the material to remove this material, that is, toproduce the non-printing area. The edge of the remaining, that is, theprinting area, should be correctly positioned and have a steep side faceso that the latter will not be inked, in order to insure a sharplydefined and accurately positioned contour in the printed reproduction ofthe line drawing. This requires as abrupt a penetration of the tool aspossible.

For practical reasons, only the extreme end portion of the tool may bemade slender; the tool will always be wider toward the top and willpresent a larger crosssection than the area being scanned. As long asthe depth of penetration of the tool is small, rapid penetration of theslender tool tip is possible without causing crowding effects. This istrue of the graving method heretofore employed. However, with the greatdepths of penetration required for the deep-graving contemplated herein,the wide stem of the tool would damage the edge of the remaining(unrelieved) printing area during its working stroke. Even if noprinting element (that is, dark portion) lies ahead in the direction ofscanning, so that from this point of view the tool could indeed bepermitted to penetrate deeply, such deep-graving might still damageprinting areas that remained at opposite sides of the path of the tool.Therefore, in accordance with one feature of the invention, the initialportion of the depression is graved with the normal depth ofpenetration, and the deep-graving starts only afterthe tool has traveleda certain distance away from the unrelieved printing area.

As the scanning member approaches a dark portion of the original, whichis to produce an unrelieved printing portion in the form, the gravingtool can be withdrawn from the material only at a finite speed. Thus,the tool would clear the surface of the material only after the scanningspot had already left the contour of the corresponding portion of theoriginal, so that the contour of the printing area would not exactlycorrespond as to its position to the contour of the original.

To avoid this difliculty, according to the invention, the tool is raisedahead of time by the amount corresponding to the increased depth ofdeep-graving, so that it thereafter graves only at a small depth ofpenetration until it is finally withdrawn from the material, that is, upto the point where a new printing area starts. In this manner, the areasubjected to deep-graving is smaller assume than the non-printing area,just as is the case in methods employing subsequent deep-millingordeep-etching operations. Similar principles apply to electrode-typegravingtools which remove the material of the printing form with the aidof an arc. In this case, the additional depth of graving according tothe present invention is accomplished by an abrupt increase in the arccurrent.

The point of commencement of deep-graving, and the moment of premature(as it were, anticipating) raising of the tool when approaching adarkimage portion, which two factors determine the size of the deep-gravedarea of the printing form, are determined according to the invention byresorting to an additional pre-scanning of the original simultaneouslywith the graving operation. Thus, two simultaneously effective scanningsystems must be distinguished from each other: On the one hand, an areaelement of the original is isolated, having the smallest possibledimension in the direction of scanning and having a width corresondingto the width of the scanning lines. The brightness of this area elementcontrols the stroke of the graving tool in known manner and with .normalamplification; the width of the tool equals that of the lines, so thatsuccessive scanned lines and successive graved lines abut. Foridentification, this area element will be referred to as scanningelement. On the other hand, an auxiliary scanning system simultaneouslyisolates an area of the original which is larger than the scanningelement and which will be designated hereinafter as auxiliary area. Thisarea scans the surroundings of the scanning element. The brightness ofthis auxiliary area is measured by an auxiliary photoelectric cellindependently of the scanning cell. As long as dark portions of the linedrawing near the scanning element lie within the auxiliary area, thephotoelectric current of the auxiliary cell is insufficient to exceed athreshold -value in the amplifier of the auxiliary systems. However, ifboth the scanning element itself and its surroundings within the largerauxiliary area are free of dark picture portions, the light reflected bythe auxiliary area is so bright, and the photoelectric current in theauxiliary cell so strong, as to exceed the threshold value of theamplifier and to initiate an additional control of the graving tool,that is, deep-graving. Numerous techniques for establishing thethreshold value are known.

For example, the amplifier of the auxiliary cell may have I a negativelybiased thyratron tube connected thereto which becomes conductive andcauses deep graving only when the controlling voltage exceeds the fixedbias potential.

In the method just described, the line-bearing original is uniformlyilluminated. The area elements for scanning are obtained by projectingan image of the original thorugh a lens systems and limiting theeffective image area by means of apertured diaphragms of differentsizes. Thus, the brightness of the diaphragm aperture controls thephotoelectric cell arranged in back thereof. Alternatively, only onescanning system may be used, which successively and alternately scanssmall and large area elements. For this purpose, known pulsatingshutters may be employed in connection with changeover switchingdevices, for example electronic switches. As a further alternative it ispossible to project two diaphragms of different aperture size, eachilluminated by a separate light source, onto the original to produce asmall light spot serving as the scanning element, and a larger area oflight acting as the auxiliary area for scanning the environment of thelight spot. Illumination is effected intermittently, with the frequencyof illumination of the scanning element differing from that of theauxiliary area. The brightness of the two areas, which may be scanned bytwo photoelectric cells or by single common cell, can then be separatedby filters or by electrical screeners or gates in accordance with thedifferent frequencies, to control different functions.

The intermittent illumination may be effected by periodically ignitedgaseous discharge lamps or by the use of rotary sector disks. In thelast mentioned case, each path of light may have incorporated therein aseparate sector disk whose frequency differs from that of the otherdisk, or a common disk having two circular rows of apertures, withdilferent numbers of apertures in the two rows, may be used with eachrow arranged in one of the light beams. The frequency of illumination atthe same time constitutes the carrier frequency for the amplification ofthe photoelectric currents.

While the size of the auxiliary area depends upon the shape and size ofthe graving tool and upon the stroke speed and rate of scanning of thetool, its shape is of less importance. It may be circular orrectangular, with the scanning element situated at its center. However,as the prescanning or auxiliary scanning is the more sensitive, thesmaller the auxiliary area is in proportion to the details of theoriginal, it is preferable to have the auxiliary area cover only thatportion of the environment of the scanning element which is situatedforwardly and on the sides of the scanning element when considered inthe direction of scanning. In this manner, the size of the auxiliaryarea may be reduced by one-half. Since deepgraving in that case would beinitiated as soon as the scanning element left a dark portion of theoriginal, it is necessary to delay the commencement of the deep-gravingby incorporating circuit elements having a substantial time lag. Ifresistance-capacitance combinations are used, the graving operation setsin sharply at the contour of a printing area and penetrates into thematerial with a gradually decreasing speed in accordance with theexponential function by which the condenser is charged. Finally, anotherpossibility is that of illuminating the auxiliary area non-uniformity ina known manner. The effect of a light area with intensity distributionwill be discussed later with reference to the drawings.

The invention thus affords the possibility of deepgraving the printingform already during its electromechanical production with the aid of anadditional scanning operation which is relatively easy to carry out,thus avoiding the need for any subsequent graving treatment with itsconcomitant time consumption and expense.

The invention will now be described with reference to the drawings, inwhich Figs. 1 and 8 diagrammatically illustrate two scanning areasystems according to the principles of this invention;

Fig. 2 shows a portion of a line original that is scanned by systemsaccording to Fig. 1 or Fig. 8;

Figs. 3 and 4 are a front view and a side elevation respectively of acutting graver;

Figs. 5 to 7 and Figs. 9 to 11 diagrammatically represent profilesproduced in the printing form with the aid of a graver such as thatshown in Figs. 3 and 4; and

Fig. 12 is a diagram illustrating apparatus for carrying out the presentinvention.

In Fig. l, numeral 1 designates the scanning element, while 2 designatesthe circular auxiliary area in which the vicinity of the scanningelement 1 is scanned. The extent or dimension of the scanning element inthe direction of scanning is small, while at right angles thereto thedimension equals the width of a line. Scanning areas of this nature canbe obtained, for example, by projecting virtual images of apertureddiaphragms arranged in the optical path of photoelectric cell systems,and causing these images to travel along the original; alternatively,limited illuminated areas are projected by a lens system onto theoriginal and are moved along the latter.

A scanning area system such as that shown in Fig. 1 is moved along aline original, a portion of which is illustrated in Fig. 2 on anenlarged scale. In this figure, 3 designates the line elements of theline drawing. The degrees of brightness occurring upon scanning withinareas 1 and 2, are converted in a known manner into photoelectriccurrents which control the operations of a graving tool such as shown,for example, in Figs. 3 and 4 in front and side views.

The cutting graver is designated as a whole by numeral 5. The width ofthe cutting edge 4 of this tool equals the height of the scanningelement 1 as viewed in Fig. 1, that is, it equals the width of ascanning line. Normally, the graver is used in such a manner that itsstroke, or depth of penetration, equals the distance 6, but indeepgraving according to the invention, this stroke is increased by theamount shown at 7. When the scanning area combination 1, 2 travelsacross the original in the line direction designated 8 in Fig. 2, thegraver 5 will cut into the printing form a profile such as that shown inFig. 5. Numeral 9 designates the remaining, unrelieved portion of theform, which is effective in printing. The scanning element 1 first scansthe dark portion 3 of the original in the direction indicated by arrow 8in Fig. 2. The edge 4 of the graver thus overlies the surface of theprinting form and leaves the printing area 10 (Fig. 5) intact. As thescanning element 1 leaves portion 3 of the original and begins to scanthe white area 11 (Fig. 2), the graver 5 becomes operative andpenetrates the material of the printing form, producing a depression 12(Fig. 5 When the scanning element 1 reaches the next-succeeding darkportion 3 of the original, the graver 5 is withdrawn from the materialso that a further printing element 13 remains in the material.

During this entire period, the auxiliary area 2 always partly extendsinto dark portions 3 of the original so that the brightness of theauxiliary area is insutficient to initiate deep-graving.

If, however, the same scanning system moves across Fig. 2 at the leveland in the direction of arrow 14, the graver will produce a profile suchas that shown in Fig. 6. In this figure, numeral 9 again designates theunrelieved portion of the form. The scanning element 1 again first scansa dark portion 3 of the original, corresponding to the printing element10 in Fig. 6. When the scanning element 1 leaves the area 3 and entersupon the white portion 11 of the original, the graver starts to cutmaterial out of the form with the stroke (or depth) 6. As soon as theauxiliary area 2 leaves the dark portion 3 of the original and coversonly white portions thereof, the brightness of the auxiliary area 2becomes sufficient to initiate deep-graving and to increase the strokeof the graver 5 by the additional amount 7. This takes place at thepoint marked 15 both in Figs. 2 and 6. Accordingly, the non-printingportion of the form is deepened, in its central area, to such an extentthat ink cannot reach the bottom 16 of the depression 17 during theinking operation. Starting at point 18, the auxiliary area 2 againbegins to include a dark portion 3 of the original while the scanningelement 1 still remains in the white area 11. The prescanning with theaid of the auxiliary area 2 causes the deep-graving to terminate atpoint 18, the graver 5 being raised by the amount 7 so that itthereafter continues to grave at the normal cutting depth 6 until alsothe scanning element 1 enters upon the dark drawing portion 3; thegraver is then moved completely out of the form material so thatprinting area 13 is formed.

Toward the end of the scanning operation, the line indicated at 19 inFig. 2 is scanned in the direction indicated. When the scanning element1 leaves the dark portion 3 of the drawing, the graver 5 penetrates thematerial with stroke 6 (Fig. 7). Although the scanning element 1thereafter scans only white portions 11 of the original, deep-gravingnevertheless will not be initiated, as the auxiliary area 2 continuouslyincludes parts of a dark area 20 located close to the line of scanning19 (Fig. 2). The graver 5 will accordingly operate at the normal depthof penetration 6 and will cut the depression 21 (Fig. 7) withoutdamaging the portions of the form remaining unrelieved adjacent to thescanning line 19.

It will thus be seen that the additional deepening in the printing formextends over the area 22 indicated by shading in Fig. 2.

Fig. 8 represents a scanning system in which 1 again designates thescanning element. The auxiliary area 23 in this instance includes onlythat portion of the environment of 1 which is located forwardly of thescanning element 1 in the direction of scanning. Assuming that theoriginal represented in Fig. 2 is again scanned along the three scanninglines 8, 14 and 19: The graver 5 will produce a printing form, whoseprofile corresponding to scanning line 8 is identical with that shown inFig. 5. On the other hand, for scanning line 14, a profile difierentfrom that shown in Fig. 6 is obtained which is illustrated in Fig. 9.The reason is that very shortly after the scanning element 1 has leftthe dark portion 3 of the original and entered the white area 11, theauxiliary area 23 likewise will no longer include dark portions of theoriginal. Consequently, initiation of the deep-graving operation withstroke 6 plus 7 takes place immediately; however, in order to preventthe deeply penetrating tool from dam aging the edge of printing element10, the electrical connections involved in deep-graving have controlmeans with a substantial time lag incorporated therein. When usingresistance-capacitance combinations for this purpose, the graver willpenetrate into the material in accordance with an exponential functionand will thus first dig steeply into the material, with its rate ofpenetration decreasing continuously, so that the profile 24 of Fig. 9 isproduced. Withdrawal of the tool from the material takes place in thesame manner as shown in Fig. 6. Scanning along line 19 correspondsexactly to Fig. 7, as the auxiliary area 23 includes regions locatedlaterally of the scanning element 1.

In the embodiments thus far described, the slope of wall 25 (Fig. 9) isdetermined by the unretarded cutting speed of the tool.

As a further feature, the auxiliary area 2 of Fig. 1 may be given anon-uniform intensity distribution, with the intensity of illuminationdecreasing from the center (where 1 is located) toward the margin ofarea 2. If the original of Feb. 2 is scanned with such a system alongscanning lines 14 and 19, the profiles shown in Figs. 10 and 11respectively will be obtained. Conditions for scanning along line 8 willremain unchanged. In this modification, the threshold value forreleasing deep-graving must be lower whereby the additional stroke 7 ofthe tool becomes variable and dependent upon the over-all brightness ofarea 2.

When the scanning element 1 leaves area 3 of the original along line 14,the brightness of the auxiliary area 2 gradually increases up to point15 and thereafter remains constant. Thus, the depth of penetration ofgraver 5 gradually increases as shown in Fig. 10 until the full stroke26 is reached. The contour 27 of the profile is governed by thebrightness distribution in area 2. The edges 27 of the printing elements10 of the .form are slanted in a manner corresponding to that heretoforeobtained by subsequent milling followed by etching in chemigraphicprocesses.

When scanning in direction 19, the auxiliary area 2 continuouslyincludes a region 20 of the original. In this case, the brightness ofarea 2 is less than in the preceding case so that also the depth ofpenetration 28 for deepgraving is less than the depth 26 of Fig. 10,while still exceeding the stroke 6 of the normal cutting operation.Withdrawal of the tool takes place in a corresponding manner.

To insure that the deep-graving responsive to the brightness ofauxiliary area 2 will be positively prevented as long as the scanningelement 1 scans dark portions 3 of the original, the circuit associatedwith the scanning element 1 includes means for preventing pre-scanningby auxiliary area 2; for example, the control current of the 7 firstcircuit may serve to block an amplifier included in the second circuit.

Fig. 12 diagrammatically illustrates an embodiment of apparatus forcarrying out the method, so as to further explain the invention. Motor29 is drivingly connected by shaft 30 to a drum 31 on which the originalis adapted to be mounted. Shaft 30 carries a further drum 32 receivingthe blank, that is, the foil or plate which is to be cut to produce theprinting form. The drums are moved both in the direction of scanning andin line-shifting directions. A plurality of light sources 33 illuminatethe original on drum 31. The scanning element 1 of Fig. 1 is fspotted onthe original with the aid of a lens system 34 and a small-apertureddiaphragm 35, and an image thereof is projected through the further lenssystem 36 into .the photoelectric cell 37. The rotating perforated disk38 renders theexposure of cell 37 intermittent. The auxiliary area 2 ofFig. l is defined on the original with the aid of a lens system 39 and alarger-apertured diaphragm 40 and is intermittently projected intophotoelectric cell 42 through a further lens system 41 and a perforateddisk 43. In lieu of the optical systems 34 to 37 and 39 to 42, a singlescanning system comprising a single perforated disk may be used in whichthe beam of rays is divided in front of the apertured diaphragms bymeans of a semitransparent mirror.

The photoelectric current produced in cell 37 and varying with thedrawing of the original, is amplified in amplifier 44 and demodulated inrectifier 45. The rectified current is transmitted through a controldevice 46 to the graving tool 47 which cuts into the blank of theprinting form, mounted on drum 32, a faithful reproduction of theoriginal. The photoelectric current emanating from cell 42 andcorresponding to the brightness of the auxiliary area 2 is amplified inamplifier 48 and demodulated in rectifier 49. Control device 50 includesmeans having a threshold value, for example, a thyratron with negativebias, which value is exceeded only if the auxiliary area 2 is free ofdark portions of the original.

Upon excitation of the control device 50, a control current istransmitted to control device 46 and is there superimposed over thecurrent coming from 37, 44 and 45. Such superimposition may, forexample, take the form of amere addition of the control voltages, or mayinvolve mixing in a multiple-grid tube. This superimposition causes thestroke of tool 47 to be increased by the amount 7 (Fig. 3) so thatdeep-graving is effected. If device 50 is not excited because area 2includes dark portions of the original, the tool 47 will either grave atthe smaller depth 6 (Fig. 3) or will be positioned entirely out ofengagement with the material of the blank of the printing form.

In the place of device 46, the graver system may include twoenergizingcoils which are connected, independently of each other, to devices 45and 50 respectively;

Changes may be made within the scope and spirit of the appended claims.

I claim:

1. Apparatus for electromechanically working a blank to produce aprinting form for the reproduction of a line original, comprising agraving tool operable relative to said blank, first light-electricalscanning means for producing signals for the actuation of said gravingtool to penetrate into the material of said blank to a predetermineddepth along areas corresponding to. white. area elements of saidoriginal which are relatively close to respectively adjacent tonedareas, second light-electrical scanning means for the actuation of saidgraving tool to penetrate into said material to a predetermined greaterdepth along areas corresponding to white area elements which arerelatively remote from the corresponding toned areas, control means forreceiving said signals, and means connected to receive the signals fromsaid control means for actuating said graving tool in accordance withsaid signals.

, 2. Apparatus according to claim 1, wherein one of said scanning meansscans the vicinity of toned area elements only in a region lying inscanning direction ahead thereof.

3. Apparatus according to claim 1, wherein said first scanning means iseffective to scan toned area elements, said second scanning means beingeffective to scan the regions adjacent said toned area elements.

4. Apparatus according to claim 3, comprising photocell means formingrespectively part of said first and second scanning means, saidphotocell means being efiective to produce signal currents according tothe brightness of the respective area elements scanned on said original,the photocell current produced by the photocell means of said secondscanning means exceeding an adjustable threshold value only if the areascanned thereby is free of toned area elements.

5. Apparatus according to claim 4, comprising separate signal-receivingmeans cooperating with each photocell means, means for connecting saidsignal-receiving means with said control means, the current from saidphotocell means which exceeds said threshold value being operative toeffect the operation of said graving tool to penetrate into the materialof said blank to said predetermined greater depth.

6. Apparatus according to claim 4, comprising separate signal-receivingmeans cooperating with each photocell means, means for connecting saidsignal-receiving means with said control means, the current from saidphotocell means which exceeds said threshold value being operative toeffect the operation of said graving tool to penetrate into the materialof said blank by a constant amount constituting said predeterminedgreater depth.

7. Apparatus according to claim 4, comprising means for inhibiting theoperative actuation of said control means by said second scanning meansfor the duration of scanning toned area elements by said first scanningmeans.

8. Apparatus according to claim 4, wherein said signalreceiving meanscooperating with the photocell means of said second scanning meanscomprises switching means having a relatively great time constant forinterposing a delay in the operative actuation thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,943,900 Muller Jan. 16, 1934 2,063,614 McFarlane et al Dec. 8, 19362,079,970 Speed May 11, 1937 2,092,765 Losier Sept. 14, 1937 2,386,816Scholz Oct. 16, 1945 2,691,696 Yule Oct. 12, 1954

